This application generally relates to an acoustic device and, more particularly, to an electrostatic electroacoustic transducer.
With the increasing interest in compact, light-weight and low-profile electronics, many products, such as computer, communication and consumer electronic products, may be manufactured with miniature feature sizes. Down-sized electronic products or components may provide flexibility in various applications. For example, electroacoustic transducers, which may be divided into dynamic-type and electrostatic-type transducers, if properly reduced in dimensions, may facilitate their use in a relatively large device such as a loudspeaker or in a relatively small device such as a micro-speaker or earphone. Conventional electroacoustic transducers, however, may have a relatively large size with respect to their acoustic performance. Generally, a dynamic transducer that may serve as a micro speaker in a cell phone may have a thickness of approximately 3 millimeters (mm) or above and a diameter of approximately 12 mm, with a sound pressure level of approximately 80 dB measured at a distance of 10 centimeters (cm) (hereinafter denoted as 80 dB/10 cm). Furthermore, a dynamic loudspeaker may have a thickness of approximately 5 cm or above and a diameter of approximately 12.5 cm with a required sound pressure level of 85 dB/1 meter (m). Moreover, an electrostatic transducer, to satisfy the required sound pressure level of 85 dB/1 m, may be as large as two A4-size papers with a thickness of at least approximately 2 cm.
Some conventional electrostatic transducers may include an electrically conductive film between two rigid electrode plates. In operation, a direct-current (DC) bias up to hundreds of volts or above may be applied to the electrically conductive film. Such conventional electrostatic transducers may often require a power amplifier, which may be costly and bulky.